Bagworms have arrived in portions of Kansas, meaning now is the time to start scouting susceptible species for feeding damage. First noted in the Wichita area, young larvae will soon be hatching and initiating feeding here in northeast Kansas as well.
For smaller trees and for shrubs, hand picking the caterpillars and bags and dumping them in to a container of soapy water can be a quick fix. Unfortunately, this is a time consuming process and not possible with larger numbers or sizes of trees.
Fortunately, a number of insecticides are labeled for use against bagworms. Some active ingredients (trade name in parentheses) include: acephate (Orthene), Bacillus thuringiensis subsp. kurstaki (Dipel), cyfluthrin (Tempo), lambda-cyhalothrin (Scimitar), trichlorfon (Dylox), indoxacarb (Provaunt), chlorantraniliprole (Acelepryn), and spinosad (Conserve). Products differ in their efficacy and application timing. Always read and follow label directions.
The key to bagworm control has less to do with the active ingredient and more to do with the manner of application. Scout trees frequently, so application can be made when caterpillars are small. Once they are more mature and more protected by their bag, they are difficult to control. Females feed less as they prepare for reproduction, which reduces their susceptibility to spray applications and any residues as well.
Thorough coverage of all plant parts is key. Spray inside and out and from top (where bagworms commonly start feeding) to bottom, making sure the insecticide reaches all parts of the tree. Multiple applications may be required as the hatch occurs over time.
If left unchecked, bagworms can cause significant damage and ruin the aesthetic quality of plants. Plant death is possible if conditions are severe. Pay careful attention to newly transplanted small evergreens. For more information, check out K-State Research and Extension publication “Bagworms,” available online at https://www.bookstore.ksre.ksu.edu/pubs/mf728.pdf or by request from your District Extension Office.